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PAPER • OPEN ACCESS Physical, Optical and FT-IR studies of -Boro-tellurite Glasses containing BaO as modifier

To cite this article: B Srinivas et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 360 012022

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

Physical, Optical and FT-IR studies of Bismuth-Boro-tellurite Glasses containing BaO as modifier

B Srinivas, Abdul Hameed, M N Chary and Md Shareefuddin Department of physics, Osmania University, Hyderabad, TS, India

E-mail: [email protected]

Abstract. The addition of glass modifier changes the properties of host glass network. The role of Ba2+ as glass modifier has been investigated using physical, UV-Visible and FT-IR studies on xBaO-(30-x)TeO2-35Bi2O3 -35B2O3 ( where x =5,10,15,20 and 25 mole% ) glasses. X-ray diffractograms of crushed glass samples were recorded at room temperature. The absence of sharp peaks in X-ray diffractograms confirms the amorphous nature of the glass samples. (ρ) of glass samples were estimated using Archimedes principle. Physical properties such as molar volume (VM), packing density (OPD), optical basicity etc. were determined. The optical absorption spectra were recorded in the wave length range of 200–1000 nm at room temperature. From the optical absorption spectra indirect allowed optical band gap, Urbach energy, (n), dielectric constant (ɛ), reflection loss (R), molar refractivity (Rm) and metallization criteria values were evaluated. The refractive index values were decreasing while optical band gap values were increasing with increasing concentration of BaO. IR spectra were recorded in the spectral range 400 - 4000 cm–1.

1. Introduction

Borate glasses containing heavy metal (HMO) such as Bismuth , oxide and oxide have been attracting researchers to synthesis and to study structural and physical properties due to their low melting temperature, widespread glass formation range, high density, high physical and chemical stability, and nonlinear optical properties. Generally heavy metal oxides do not form glasses on their own compare to the conventional glass forming oxides due to their low field strength. In HMO containing glasses, bismuth oxide glasses have shown wide range of applications in the area of glass ceramics, reflecting windows, γ-ray absorbers, thermal and mechanical sensors, optoelectronic devices and scintillation detectors [1, 2]. High polarizable Bi3+ and asymmetry of their oxygen coordination polyhedra can assist the non-crystallization of melts [3]. On the other hand covalently bonded B2O3 is a very good glass former with interesting physical and chemical properties. 3+ Basically B2O3 glasses are insulating in nature and the B in borate crystals and glasses usually coordinates with either three or four oxygen atoms forming [BO3] or [BO4] structural units. Borate glass is well-known and best choice as optical material for its high transparency, low and high thermal stability [4]. A.M. Abdelghany et.al [5] have prepared and characterized the borate glasses containing SrO substituting both CaO and NaO for their bioactivity or bone bonding ability. They have confirmed the formation of nodular texture of phosphate (hydroxyapatite) and transform to micro-grains with increase of SrO. Tellurite glasses have paid extensive attention as

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

promising candidates for optical fibers, ultra-fast optical switching devices and high non-linear optical devices because of their low-phonon energy, high refractive index, high polarisability of the non- bonding electron lone pair of Te4+ ions and low crystallization ability [6-8]. However, it must be noted that pure TeO2 does not possesses its own glassy network, under normal melting conditions. Hence addition of network modifiers or glass forming oxides is needed to form tellurite-based glasses [9]. Structural and physical properties of glasses can be altered by the addition of a network modifier such as alkali or alkaline earth oxides and sometimes both alkali and alkaline earth oxide combinations. These network modifier oxides generate non-bridging (NBO) in the glass network by breaking the bridging oxygen bonding.

2. Experimental

Bismuth-Boro-tellurate glasses containing BaO as network modifier were prepared with the composition xBaO-(30-x)TeO2-35Bi2O3-35B2O3 (with the glass codes as, x=5; BTBiB1, x=10;BTBiB2, x=15; BTBiB3; x=20; BTBiB4 and x=25;BTBiB5) by melt quenching technique. Analytic reagent grade chemicals of highest purity BaO, TeO2, Bi2O3 and B2O3 were used as starting materials which are thoroughly mixed in an agate mortar for 20 min. The batch materials were taken in porcelain crucibles and placed in an electrically heated muffle furnace kept around 1200 to1280 K for about one hour, until a bubble free, clear and homogeneous melt was obtained. The homogeneous melt was then quickly poured onto a stainless steel plate and pressed with another stainless steel plate, both were maintained at 500 K. The obtained glass samples were kept at 500K for 5h to relieve the thermal strains in the glass. Density measurements were carried out at room temperature using the Archimedes method with xylene as the immersion liquid. The X-ray diffractograms were recorded at room temperature using the Philips X-ray diffractometer with Kα tube target and filter operated at 40 kV, 30 mA. The optical absorption spectra of all the glass samples were recorded at room temperature on a UV–VIS spectrophotometer (model JASCO V 570) in the wavelength range 20 0–1000 nm. The FTIR spectra were recorded at room temperature by using a Perkin Elmer Frontier FTIR in the wave number range (400–4000 cm−1).

3. Results and discussion

3.1 X-ray diffraction

XRD patterns of xBaO-(30-x)TeO2-35Bi2O3-35B2O3 glasses are shown in figure 1The absence of characteristic peaks indicated that all the glass samples are amorphous in nature.

3.2. Physical properties The of all of the glass samples were estimated using the formula

 w     air  0.865 (1)    wair  wxylene  where Wair and Wxylene are the weights of the glass sample in air and xylene, respectively, and 0.865 g/cm3 is the density of the xylene at room temperature. The molar volume of the glass composition was calculated using the formula x M V   i i (2) m  th where xi is the molar fraction, Mi is the molecular weight of the i component of the glass and ρ is the density of the glass. The Molar volume relates directly to the spatial distribution of the oxygen in the glass network. The Density and molar volume values are given in table 1. From the table 1it was found

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

that the density increases from 5.73 to 6.12 g/cm3 with the increase of BaO content. This could be due 3 3 to the higher density of BaO (ρ = 5.72 g/cm ) than that of TeO2 (ρ = 5.67 g/cm ). Figure 2 shows the variation of Density (ρ) and Molar volume (Vm) as a function of BaO content. From the figure 2 it was found that the density and molar volume shows opposite behavior [10, 11]. Oxygen packing densities (OPD) of glass samples were calculated using the expression given below and the values obtained were tabulated in table 1.  OPD=  O (3) M n

Here On is total number of oxygen atoms per . From the table 1 it was observed that the OPD values were found to decrease from 59.28 to56.86 mol/l. This decrease in OPD values may be attributed to the increase in molecular weight of the glass.

6.2 45.0

44.8

6.1 44.6

44.4 BTBiB1 6.0 44.2

44.0

BTBiB2 5.9 43.8

BTBiB3 Density(g/cc) 43.6

5.8 MolarVolume (cc) intensity (arb.units) intensity BTBiB4 43.4

BTBiB5 5.7 43.2 Density Molar volume 43.0 10 20 30 40 50 60 70 80 5 10 15 20 25 2 BaO mole %

Figure 1. XRD patterns of xBaO-(30-x)TeO2- Figure 2. Variation of density and molar

35B2O3-35Bi2O3 glasses volume with BaO content

3.3. Optical Band Gap and Urbach Energy The optical absorption spectra of the glass samples are shown in figure 3. The power law region is clearly observed in absorption spectra and fundamental absorption edges are not sharp. This is the characteristic feature of amorphous glass samples. From table 1, it was observed that that the fundamental absorption edge shifts to higher wavelength side with an increase of BaO content. Absorption coefficient near the edge of each curve was determined by using the relation

  1/ tlogI0 / I (4) where log (Io/I) is the absorbance, I0 and I are the intensities of incident and transmitted light respectively. According to Davis and Mott[12], the absorption co-efficient as a function of photon energy is given by the relation n   B(h  Eopt) / h (5)

where Eopt is the optical band gap energy, B is the constant related to the extension of the Urbach tail and „n‟ take the values of 2, 1/2, 3, and 3/2 depending on the nature of electronic transitions responsible for absorption. For amorphous materials, indirect transitions are valid according to Tauc‟s 1/2 relation [13]. The values of Eopt were obtained by extrapolating to (αhv) =0 for indirect transitions. 1/2 [(αhν) Vs hν are plotted in (figure 4)], to find optical band gap energies. Eopt values were found to increase with an increase of BaO content. In glass and amorphous materials there exist band tailing in

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

the forbidden energy band gap. The extent of this band tailing is a measure of the disorder in the material and can be estimated by using the Urbach equation [14, 15] given by, ()  C exp(h / E) (6) where, C is a constant and ∆E is the width of band tail also known as Urbach energy. The lack of crystalline long range order or the presence of defects in the amorphous materials is associated with a tailing of density of states [16]. Urbach energies (∆E) are calculated by taking the reciprocals of slopes of linear portion in lower photon energy regions of these curves and are shown in figure 5 Urbach energy (∆E) provides a measure of disorder in the amorphous and crystalline solids. Smaller is the value of Urbach energy, greater is the structural stability of the glass system. In the present glass system Urbach energies are in the range of 0.19eV to 0.27eV. The smaller values of Urbach energies show high stability of the prepared glasses. Refractive index of the xBaO-(30-x)TeO2-35Bi2O3 -

35B2O3 glasses is decreasing with increase of BaO content. The polarizability of barium ion is larger than the other cations [17]. High refractive index is attributed to the higher polarization of BaO. According to the Herzfeld theory [18] of metallization the valence electrons, which before have been quasi-elastically bound to their atoms, are now set free via mutual polarization in the condensed state and the solid material becomes a metallic conductor. In this regard the following criterion appears to be a necessary condition to predict the metallic or non-metallic nature of solids i.e Rm /Vm > 1 (for metals) and Rm/Vm < 1 (for nonmetals). The present reported values of Rm /Vm are in the range of 0.3624 to 0.3745. As BaO concentration is increasing in glass network an increased tendency to metallization was noticed. The smaller value of M (metallization) of these glasses indicated that the width of both conduction band and valence band increases resulting in narrow band gap.

12 BTBiB 1 BTBIB 1 2.4 BTBiB 2 BTBIB 2 BTBiB 3 10 BTBIB 3 BTBiB 4 2.0 BTBIB 4 BTBiB 5 BTBIB 5 8

1.6 1/2 ) 6

1.2 

h

 (

0.8 4 Absorbance(arb.units)

0.4 2

0.0 200 400 600 800 1000 0 1.6 2.0 2.4 2.8 3.2 3.6 wavelength (nm) Photon energy (eV)

Figure 3. Optical absorbance spectra of Figure 4. Plot of (αhυ)1/2 as a function hυ of for xBaO-(30-x)TeO2-35Bi2O3-35B2O3 the present glasses

3.4. Optical Basicity In the development of the Lewis acid- principles Duffy and Ingram have made great contribution by introducing the “optical basicity” concept. This concept is very useful for quantitative evaluation of the acid-basic properties of glasses, alloys, slags, molten salts, etc. The degree of polarization plays an important role to transfer electron density from oxygen to surrounding cations. High polarizable cations such as P5+, Si4+, B3+ ions decreases the donor nature of oxygen by influencing the electron cloud of oxygen. According to the Duffy [19], the theoretical optical basicity (Λth), for the present glasses is calculated using the following formula

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

2 2 ∧th =XBaO∧BaO+XTeO ∧Teo + XBi2O3∧ Bi2O3+ XB2O3∧ B2O3 (7)

Where XBaO, XTeO2, XBi2O3 and XB2O3 are the contents of individual oxides in mole%. ∧BaO , ∧Teo2, ∧ Bi2O3 and ∧ B2O3 are the theoretical optical basicity values corsponding to the each oxides have been taken from the literature . The theoretical optical basicity Λth values calculated using above equation for the brium bismuth boro-tellurate glasses are presented in table 1. It is found that the theoretical optical basicity decreases slightly with increasing BaO content.

3.5 BTBiB1

BTBiB2 BTBiB5 BTBiB3 BTBiB4 699 429 3.0 BTBiB5 1280 1028 860 BTBIB4 428 690 867 1278 1032

BTBiB3

ln 2.5 1024 863 698 427

Transmitance(a.u) 1280 BTBiB2

424 863 1276 1035 686 BTBiB1 2.0 1282 1042 868 684 424

1600 1400 1200 1000 800 600 400 2.0 2.5 3.0 3.5 -1 Photon energy (eV) Wavenumbers (cm )

Figure 5. Urbach energy plot of xBaO-(30- Figure 6. FTIR spectra of xBaO-(30-x)TeO2- x)TeO2-35Bi2O3-35B2O3glasses 35Bi2O3-35B2O3glasses

Table 1. Physical and optical parameters of xBaO-(30-x)TeO2-35Bi2O3 -35B2O3 glass system. Physical & optical Glass codes Parameters BTBiB-1 BTBiB-2 BTBiB-3 BTBiB-4 BTBiB-5 Density (ρ) (g/cc) 5.73 5.81 5.90 6.06 6.12 Molar volume (Vm) (cc/mol) 44.70 44.40 44.05 43.20 43.09 Oxygen packing density (mol/l) 59.28 58.56 57.89 57.87 56.86 Cut-off wavelength (nm) 441 442 445 451 458 Indirect optical band gap (eV) 2.63 2.72 2.75 2.75 2.81 Urbach energy E (eV) 0.20 0.27 0.20 0.19 0.20 Refractive index (n) 2.51 2.48 2.47 2.47 2.45 Dielectric constant (ε) 6.28 6.13 6.08 6.09 6.01 Reflection loss (R) 0.1844 0.1803 0.1790 0.1792 0.1769 −3) Molar refractivity (Rm) (cm 28.50 28.01 27.70 27.19 26.95 Metallization (M) 0.3624 0.3690 0.3711 0.3707 0.3745 Theoretical optical basicity (Λth) 0.1602 0.1587 0.1571 0.1556 0.1540

3.5 IR spectra

The infrared transmittance spectra of the glasses with composition xBaO-(30-x)TeO2-35Bi2O3 -

35B2O3 are shown in figure 6 From the figure it was observed that the absorption bands were found around 428 cm-1, 690 cm-1, 863 cm-1, 1030 cm-1,and 1280 cm-1 for all the glass samples. The small and -1 feeble absorption band found around 428 cm is assigned to the Bi-O bond in BiO6 polyhedra [10]. -1 The prominent band found around 690 cm is due to TeO3 (tp) trigonal pyramidal units [20]. Another prominent band observed around 863 cm-1 is attributed to the vibration of tri, penta and diborate -1 groups of BO4 tetrahedra [21]. A shallow broad absorption band found around 1030 cm is attributed to B-O stretching vibrations of tetra hedral BO4 units [22]. Another shallow broad absorption band

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Second International Conference on Materials Science and Technology (ICMST 2016) IOP Publishing

IOP Conf. Series: Materials Science and Engineering1234567890 360 (2018)‘’“” 012022 doi:10.1088/1757-899X/360/1/012022

observed in the region 1280 cm-1 is attributed to the asymmetric stretching vibrations of B-O in trigonal BO3 units [22]. 4. Conclusions The density values increases from 5.73 to 6.12 g/cm3 with the increase of BaO content. The density and molar volume shows opposite behavior. Refractive index of the present glasses is decreasing with increase of BaO content. High refractive index values are due to the higher polarization of BaO. From the infrared transmittance spectra of the glasses, it is observed that the -1 -1 1 absorption bands around 428 cm is assigned to the Bi-O bond in BiO6 polyhedra, 690 cm is is due -1 to TeO3 (tp), 863 cm is attributed to the vibration of tri, penta and diborate groups of BO4 tetrahedra, -1 -1 1030 cm is attributed to B-O stretching vibrations of tetra hedral BO4 units and 1280 cm band is due to asymmetric stretching vibrations of B-O in trigonal BO3 units. Acknowledgements The authors would like to thank The Head, Department of Physics, Osmania University for providing laboratory facilities. One of the authors B.Srinivas would like to thank the UGC, BSR- RFSMS, New Delhi, for providing financial assistance. References: 1. E. Culea, L. Pop, P. Pascuta, M. Bosca 2009 J. Mol. Struct. 924 192 2. A. Agarwal, V.P. Seth, P.S. Gahlot, S. Khasa, P. Chand 2003 J. Phys. Chem. Solids. 64 2281 3. L. Baia, R. Stefan, J. Popp, S. Simon, W. Kiefer 2003 J. Non-Cryst. Solids, 109 324 4. S. Mohan, K.S. Thind, G. Sharma, Braz 2007 J. Phys. 37 (4) 1306. 5. A.M. Abdelghany, M.A. Ouis, M.A. Azooz, H.A. ElBatal, G.T. El-Bassyouni 2016 Spectrochim. Acta A Mol. Biomol. Spectrosc. 152 126 6. M.A. Villegas, J.M. Fernández Navarro 2007 J. Eur. Ceram. Soc. 27 2715 7. X. Shen, Q.H. Nie, T.F. Xu, Y. Gao 2005 Spectrochim. Acta A Mol. Biomol. Spectrosc. 61 2827 8. Abdeslam Chagraoui, Abdelmjid Tairi, Kaltoum Ajebli, Hanane Bensaid 2010 J. Alloys Compd. 495 67 9. El-Mallawany RAH. 2002 Tellurite glasses handbook. Boca Raton/London/NewYork/Washington, DC: CRC Press 10. M. Subhadra, P. Kistaiah 2012 Vibrational Spectroscopy 62 23 11. P.P. Pawar, S.R. Munishwar, R.S. Gedam 2016 J. Alloys Compd. 660 347 12. E A Davis and N F Mott 1970 Phila. Mag., 22 903 13. N Elkhoshkhany, R Abbas, R El-Mallawany and A J Fraih 2014 Ceramics International 40 14477. 14. F Urbach 1953 Phys. Rev. B. 92 1324. 15. S Sanghi, S Sindhu, A Agarwal and V P Seth 2014 Radiations Effects & Defects in solids :Incorporating Plasma Science and Plasma Technology 159 369. 16. N Elkhoshkhany 2014 J. Chem. Chem. Eng. 8 11. 17. V Dimitrov and S Sakka, 1996 J. Appl. Phys., 79 1736. 18. Herzfeld K 1970 Phys. Rev. B, 2 2045 19. J.A. Duffy 1989 Phys. Chem. Glasses 30 1 20. S. Suresh , P. Gayathri Pavani , V. Chandra Moulim 2012 Materials Research Bulletin 47 724 21. I. Kashif, A.A. Soliman, H. Farouk, M. El-Shorpagy, A.M. Sanad 2008 Physica B 403 (2008) 3903 22. Chandkiram Gautam, Avadhesh Kumar Yadav, and Arbind Kumar Singh 2012 ISRN Ceramics 2012 17

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